Difference between revisions of "Linux-AWK/C2/Basics-of-awk/English"

Learning Objective

awk command.

We will do this through some examples.

System requirement

• Ubuntu Linux 12.04 OS
• GNU BASH v. 4.2.24

Please note, GNU Bash version 4 or above is recommended to practice this tutorial.

Introduction

The awk command is a very powerful text manipulation tool.

It is named after its authors, Aho, Weinberger and Kernighan.

It operates at the field level of a record.

So, it can easily access and edit the individual fields of the record.

For demonstration purpose, we use the awkdemo.txt file.

Let us see the contents of awkdemo.txt file.

CTRL + ALT and T keys simultaneosuly on your keyboard.

type:

"awk '/Pass/ {print}' awkdemo.txt" [enter]

Type:

awk space (within single quote) (front slash) ‘/Pass (front slash)/(opening curly bracket) {print (closing curly bracket)} (after the quotes) space awkdemo.txt

Press Enter

All the lines of the awkdemo where Pass occurs are printed.

The action here is print.

"awk '/M[ei]*ra*/ {print}' awkdemo.txt" [enter]

Say we want to print records of students with name Mira.

awk space '/M opening square bracket [ ei closing square bracket ]*ra */{ print}' space awkdemo.txt

Press Enter.

Thus entries with more than one occurrence for i, e and a will be listed.

For ex.

• Meera
• Mira
• Meeraa

Which means we can match multiple patterns separated by a PIPE.

"awk '/civil|electrical/ {print}' awkdemo" [enter]

awk space (in single quotes)(front slash) ‘/civil (vertical bar)|electrical (front slash)/{print}' awkdemo.txt

Press Enter.

Now entries for both civil and electrical are shown.

awk has some special parameters to identify individual fields of a line.

$1(Dollar 1) would indicate the first field.

Similarly we can have $2, $3 and so on for respective fields.

$0 represents the entire line.

Type: cat awkdemo.txt

In this case PIPE is called a delimiter.

A delimiter separates words from each other.

A delimiter can also be a single whitespace.

To specify a delimiter, we have to give - capital F flag followed by a delimiter.

“awk -F "|" '/civil|electrical/ {print $0}' awkdemo ” [enter]

So we can write the last command as:

awk space minus capital F space within double quotes PIPE space within single quote front slash civil PIPE electrical front slash within curly braces print space dollar0 space awkdemo.txt

Press Enter

This print the entire line since we have used $0.

“awk -F"|" '/Pass/ {print $2, $3}' awkdemo” [enter]

We will replace $0 with $2 and$3 in the above command.

Press Enter

Only two fields are shown.

NR,$2,$3 }' awkdemo” [enter]

We can also provide a serial number by using a builtin variable NR.

We will see more about builtin variables later.

Now type:

awk space -F”|” space '/Pass/{printf “%4d %-25s %-15s \n”, NR,$2,$3 }' space awkdemo.txt

Press Enter.

We see the difference.

Here the NR stands for number of records.

Records are integers, hence we have written %d.

Name and Stream are strings. So we have used %s.

Here 25s will reserve 25 spaces for Name field.

15s will reserve for Stream field.

The minus sign is used to left justify the output.

Let us move back to our slides.

Let us summarize.

In this tutorial we learnt

To print using awk

Regular expression in awk

To list the enteries for a paritcular stream

To list only the second and the third fileds

To display a formatted output

Display roll no., stream and marks of Ankti Saraf

Acknowledgement Slide

It summarises the Spoken Tutorial project

If you do not have good bandwidth, you can download and watch it

Spoken Tutorial Workshops

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, please write to

contact@spoken-tutorial.org

Acknowledgement

It is supported by the National Mission on Education through ICT, MHRD, Government of India

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro

Display the previous slide only and narrate this line.

This is Ashwini Patil from IIT Bombay signning off. Thank you for joining.